1. Field of the Invention
The present invention relates to a transponder and a system thereof, and more particularly to charging a secondary battery and a capacitor such as a large scale capacitor which is used as a power source.
2. Description of the Related Art
When a tire is distinguished or internal pressure, temperature, a number of revolutions or the like of a tire are going to be obtained, there is known technique of a type in which electric oscillation energy is received from a position spaced apart from a specific tire to transmit a signal from a transponder embedded in the tire.
Also, the transponder is composed of an integrated circuit and an outer shell for protecting the integrated circuit, and has various shapes such as a small coin shape or a cylindrical column shape.
An example of technique of this sort is disclosed in Japanese Utility Model Laid-Open No. 2-123404 specification. According to this technique, an embedded position of the tansponder in a tire is set to the central portion at the tip end level of a carcass ply wound-up portion or on the outer surface of the carcass ply of the pad-less portion.
Also, as another example, there has been disclosed a pneumatic tire with a transponder fitted in Japanese Utility Model Laid-Open No. 7-13505 specification. This has been obtained by improving the above described technique. In this pneumatic tire, there is provided a transponder housing pocket in a protrusion provided on the inner peripheral surface of a bead portion of a troidal-shaped tire. More specifically, the protrusion having the transponder housing pocket is provided on the bead portion having few movement during traveling on the inner peripheral surface of the tire, which is off a portion constituting the tire. For this reason, the tire will not be adversely affected. Further since the transponder is capable of freely entering and going out of the pocket, it is possible to freely inspect the transponder housed or replace in case of necessity.
In a transponder according to the above described conventional example, however, since a battery is used in order to operate an electronic circuit within in most cases, when the battery becomes exhausted, the transponder ceases operation. For this reason, it is necessary to replace the battery periodically, and this replacement operation takes a great deal of time and labor. Also, in the transponder embedded within the tire, the battery could not be replaced.
The present invention has been achieved in views of the above described problems, and is aimed to provide a transponder, an interrogator and a system thereof in which a secondary battery and a capacitor such as a large scale capacitor are capable of being easily charged from the outside. It is another object of the present invention to provide a transponder, an interrogator and a system thereof in which charging can be easily performed from the outside and electric power consumption of the capacitor is restrained.
A transponder system according to the present invention has a transponder and an interrogator, and has energy supplying means for radiating an electromagnetic wave of a second frequency from an antenna. This antenna is provided in at least one of a station and a parking lot for the vehicle. Further, the energy supplying means radiates an electromagnetic wave to the transponder only when a vehicle equipped with the transponder is at a station or a parking lot for the vehicle. For this reason, when a vehicle equipped with a tire with a transponder is in a station or a parking lot for the vehicle, the transponder system according to the present invention radiates an electromagnetic wave of a second frequency from an antenna by means of the energy supplying means to thereby charge the capacitor for the transponder.
Also, the transponder according to the present invention receives a question signal from the interrogator through the use of the first frequency to convert electromagnetic wave energy of the signal of first frequency received into electric energy by means of first energy converting means. This electric energy operates a central processing unit and transmission means of the transponder. The central processing unit of the transponder reads storage information in the information storage means, and generates an electric signal for representing answering information to the question signal of the first frequency to output to the transmission means. The transmission means transmits the answering signal on the basis of the electric signal from the central processing unit.
Also, the transponder according to the present invention converts electromagnetic wave energy of the second frequency received by the second receiving means into electric energy by means of the second energy converting means. This electric energy charges the capacitor. Electric power accumulated in the capacitor is used as an auxiliary power source or a main power source for operating an additional circuit whose electric power consumption is larger than the main circuit. In this case, since the second frequency has been set to a frequency lower than the first frequency, the capacitor can be charged by receiving the electromagnetic wave of the second frequency even when communication is performed with the interrogator, and the energy can be transmitted at higher efficiency than when the first frequency is used. Also, as the first frequency, a high frequency having fast data transfer speed can be used.
The transponder according to the present invention has, as an additional circuit, a sensor portion for detecting predetermined physical quantity within the tire to output the detection result through an electric signal. Further, the central processing unit has means for taking in the detection result by the sensor portion to include into the answering information. For this reason, the transponder according to the present invention is capable of including physical quantity such as pneumatic pressure and temperature within the tire which has been detected by the sensor portion into the answering information to transmit. Further, the transponder according to the present invention has, in the sensor portion, at least one of a temperature sensor and a pneumatic pressure sensor. For this reason, the transponder according to the present invention is capable of transmitting answering information including information on the temperature and internal pressure of the tire which has been detected by the temperature sensor and the pneumatic pressure sensor.
Also, the transponder according to the present invention uses electric energy charged in the capacitor only to drive the sensor portion. Further, the transponder according to the present invention carries current to the sensor portion from the capacitor only for predetermined time until the physical quantity is detected by the sensor portion and the detection result is taken in the central processing unit. For this reason, the electric energy accumulated in the capacitor is consumed only in a necessary and minimal amount. In the present invention, the capacitor is constituted by a secondary battery or a large scale capacitor. Further, the capacitor has charging capacity capable of charging electrical energy sufficient to obtain detection result by the sensor portion at least once.
The transponder according to the present invention has means for detecting whether or not it is necessary to charge the capacitor, and means for including a signal for requesting charging in an answering signal for transmitting when charging is required on the basis of this detection result. For this reason, for example, when an interrogator or a charging device receives the answering signal including the signal for requesting charging or the signal for requesting charging, the electromagnetic wave of the second frequency is radiated from the interrogator or the charging device to the transponder to automatically perform charging.
The transponder according to the present invention has a loop coil-shaped antenna as an antenna for receiving electromagnetic wave of the second frequency. For this reason, an antenna for transmitting electromagnetic wave of the second frequency is a similar loop coil-shaped antenna, and when these two antennas are approached to each other such that their coil axes substantially coincide with each other, electromagnetic induction by the Lenz""s law is performed, and the energy can be transferred more effectively.
On the other hand, the interrogator according to the present invention transmits a question signal to the transponder through the use of an electromagnetic wave of the first frequency by question signal transmission means, and receives an answering signal from the transponder to this question signal by means of receiving means. Further, the interrogator according to the present invention transmits, by means of the energy supplying means, an electromagnetic wave of the second frequency that is different from the first frequency to transfer the energy to the transponder through the electromagnetic wave of this second frequency.
Only when a signal for requesting supply of energy through electromagnetic wave of the second frequency is included in the answering signal, the interrogator according to the present invention has driving control means for driving the energy supplying means. For this reason, only when an answering signal including a signal for requesting charging is received, the energy supplying means is driven to radiate the electromagnetic wave of the second frequency to the transponder.
Also, in the present invention, as an antenna for transmitting the electromagnetic wave of the second frequency to the transponder from the interrogator, a coil-shaped or a volute loop antenna is used. For this reason, an antenna for receiving the electromagnetic wave of the second frequency of the transponder is a similar loop antenna, and when these two antennas are approached to each other such that their coil axes substantially coincide with each other, electromagnetic induction by the Lenz""s law is performed, and the energy can be transferred more effectively.
Also, the interrogator according to the present invention has means for detecting existence of the transponder within an area in which energy can be supplied, and driving control means for driving the energy supplying means when there exists the transponder within the area on the basis of this detection result. For this reason, when the existence of the transponder within the area in which the energy can be supplied is detected by means of the interrogator, the energy supplying means is driven and the electromagnetic wave of the second frequency is automatically transmitted from the interrogator to the transponder.
Also, according to the present invention, size and shape of a casing in which each component of the interrogator has been housed are made into portable size and shape, whereby it has been made possible to easily carry it.
Further, according to the present invention, the first frequency is set to a frequency above a short wave region to thereby improve the data transfer efficiency, and the second frequency is set to a frequency below a medium wave region to thereby improve the energy transfer efficiency. Further, according to the present invention, the second frequency is set to a frequency below 200 kHz to thereby further improve the energy transfer efficiency. Also, according to the present invention, so as to prevent communication using the first frequency from being disturbed by higher harmonic of the second frequency, the first frequency has been set to a frequency different from frequencies equal to the integer multiple of the second frequency.